CA1327175C - Stable gene amplification in prokaryotic chromosomal dna - Google Patents

Abstract

ABSTRACT

Transformed prokaryotic hosts are provided compris-ing two or more copies of a DNA sequence stably maintained in their chromosome, said sequence comprising a gene encoding a polypeptide of interest, wherein said copies are separated by endogenous chromosomal DNA sequences. Methods are also pro-vided for producing said transformed host strains. Said transformed host strains are capable of increased production of the polypeptide of interest compared to host strains which already produce said polypeptide. Preferred host strains are Bacillus novo species PB92 which produces a high-alkaline pro-teolytic enzyme and Bacillus licheniformis T5 which produce a thermostable alpha-amylase, and mutants and variants of said strains. Preferred polypeptide encoding genes are the pro-tease encoding gene originating from Bacillus PB92 and the alpha-amylase encoding gene originating from Bacillus lichen-iformis strain T5.

Description

~-- 132717~ ~:

STABLE GENE ~MPLIFICATION IN CHROMOSOMAL DNA
OF PROKARYOTIC MICRQORGANISM~

INTRODUCTION
Technical Field The field of this invention relates to prokaryotic ~ ' cells in which stable gene amplification is obtained by scat-tered non-tandem integration of at least two copies of a de-fined DNA sequence into the chromosome of said prokaryotic cell. ~-, - BRIEF DESCRIPTION OF THE DRAWINGS

Figures lA-D are schematic representations of four ways for integration of extrachromosomal DNA sequences into ~ the chromosome of prokaryotic microorganism.
-~ : T iS the target sequence, i.e.~DNA sequences pre-sent on chromosome and plasmid, between which homologous re- ~ ~, Z0 combination an take place.
S stands for the DNA sequence to be integrated in~
, the chromosome.
M stands for a marker gene sequ'ence used~for the selection of recombinant strain.
25 , Figures ZA~and ZB are schematic representations of ~'-two~ways for obtaining stable gene amplification in a prokary-- -- otic chromosome.
Figuré 3 shows the results of histidine/MOPS gel ~',, electrophoresis performed on supernatant from cultures of B.
30'~ subtilis DB104 containing pUB110 and pM58, respectively,~com-~
,pared with several subtilisins': , ~
lane 1: Carlsbera subti'lisin lane 2: Bacillus PB92 protease lane 3: Bacillus',subtilis subtilisin ~35 ~ lane 4: ; Bacillus~subtilis DBIo4 (pM58) lane 5: ~ Bacillus subtili~ DB104 (pUBllO ) Figure 4 shows the restriction map of plasmid pM58.
Furthermore, the~,sequencing strategy is shown in the upper 32717~ -part of the figure. The arrowed solid lines represent the fragments cloned ln the phage M13 vectors mplO, mpll and mpl8. The lower part of the figure shows the sequencing strategy using ten oligonucleotides located at regular dis-tances on the protease gene.
Figure 5 shows the nucleotide sequence of the cod-ing strand correlated with the amino acid sequence of Bacil-sg2 serine protease. Promoters (Pl, P2), ribosome bind-ing site (rbs) and termination regions (term) of the DNA se-quence are also shown. The numbered solid lines represent ;~
the location of the ten oligonucleotides used for sequencing.
Figure 6A shows the construction of plasmid pE194~-neo.
Figure 6B shows the construction of plasmid pMAX-4. -~
Figure 7A digests prepared with HindIII of chromo-somal DNA of the strains PB92, PBT109 and PBT108 were sub-jected to electrophoresis on a 0.5% agarose gel, transferred -~
to nitrocellulose as described by Southern and hybridized with 32p labeled nick-translated pM58 DNA. The figure shows -~
an autoradiograph.
Figures 7B and 7C illustrate the integration events occurring in case of homologous (B) recombination and illegi- ~-timate (C) recombination between pMAX-4 and the Bacillus PB92 chromosome. :
Figure 8 shows the construction of integration vec-tor pElatB. ~
Figure 9A illustrates the integration of plasmid ~ -pElatB into the chromosome of B. licheniformis strain T9 re-sulting in B. licheniformis strain TB13.
-~ 30 Figure 9B illustrates the chromosomal recombination of the B. licheniformi~ strains TB13 and T5 upon protoplast fusion of these strains, resulting in B. licheniformis strain ; ~`
T13F.
Figure 10 shows a chromosomal analysis of nine dif-ferent colonies isolated from a fermentation of strain T13F ~-as described in Example 11. Isolated chromosomal DNA was di-gested with EcoRI separated on 0.8~-agarose gels and blotted B; onto nitrocellulose. Hybridization of the blot was performed ''"'." :.. ~

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with 32P-labeled nick-translated pElats DNA. The figure shows an autodiagram. The upper arrow indicates the position where an EcoRI DNA fragment of about 15kb migrates which con-tains the entire pElatB sequence that was integrated into the S chromosome on a location not adjacent to the original alpha-amylase gene, as depicted for strain TB13 in Figure 9A. The lower arrow indicates the position where an EcoRI DNA frag-ment of about 33kb migrates which contains the entire alpha-amylase gene originally present in B. licheniformis strain T5 (see also Figure 9B). The following DNA samples were ana-lyzed:
lane 1: Bacillus licheniformis T5 DNA
lane 2: Bacillus licheniformis Tsl3 DN
lane 3: sacillus licheniformis T390 D~A -~
lane 4: DNA from a neomycin-sensitive derivative of Bacillus licheniformis T390, isolated after fermentation, as described in ~-Example 12 lane 5: Bacillus licheniformis T13F DNA
lane 6-14:DNA from 9 different colonies isolated from a fermentation of strain T13F as described in Example 12.

Backaround Bacilli have been widely used for the production of industrially important enzymes such as alpha-amylase, neutral protease and alkaline or serine proteases (cf. Debabov, "The Industrial Use of Bacilli", in: The Molecular Biology of Ba-cilli, Acad. Press, New York, 1982). Improvement of produc-tion of 13acillus enzymes can be achieved both by classical genetic techniques, such as mutation and subsequent selec-tion, and by modern molecular biological techniques. In the latter case, several ways of obtaining high levels of expres-sion of homologous and heterologous genes in certain prokary-otic and eukaryotic microorganisms by genetic engineering have been well documented.
One of the approaches to achieve high level expres-` 132717~

sion of a gene is to provide the gene with efficient regula-tory sequences. Another approach, often used in co~bination with the first approach, is to increase the copy number of ;
the gene in question. Amplification is primarily achieved by inserting the g~ne into a multicopy extrachromosomal DNA mole-cule such as a plasmid. However, a significant drawback of using plasmids as vectors for expressing and amplifying gen- ~-etic information has been their instability. For large scale use, stability of the amplified gene is a prerequisite for maintaining high level production of the expression product encoded by the amplified gene, as many cell divisions have to take place before sufficient biomass is formed for obtaining substantial product formation.
Instability is encountered in two forms~
segregational instability, where loss of the plasmid occurs ~ -during cultivation; and structural instability, where a part of the plasmid is deleted. Segregational instabili~y can occur, for example, when a host cell is harbouring a vector carrying a gene that is overexpressed. Generally there will be selective pressure towards cells that have lost the capa-city to overexpress the gene, since overexpression is an un~
favorable property for the transformed host cell. A large amount of metabolic energy is spent on the overexpressed gene product, which negatively influences the cells~ competitive- ;
ness (growth rate) with host cells not likewise overexpres-sing.
A method used to counter segregational instability is to select for cells containing multicopy plasmids which carry genes which confer an advantage on the plasmid contain-ing cell, for example, conferring resistance to an antibiotic and then to add the relevant antibiotic to the fermentation :~-broth. However, antibiotics are generally not a useful selec-tion means in large scale commercial production processes due to regulations concerning the approval of the fermentation ' 35 process or the product itself.
, Another method used to minimize plasmid loss due to segregational instability is to insert a gene which is func-tionally essential for the host cell into the vector molecule -~

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., ~.~-:

:: 132717~

(Ferrari et al., Biotechnology 3 (1985) 1003-1007). However, this method does not ensure structural stability of the vec-tor.
Techniques used to solve the problem of structural plasmid instability have included avoiding expression of the gene during the phase of exponential growth, for example, by using regulatory sequences such as temperature-sensitive regu-latory sequences, and integration of the exogenous DNA into the host cell chromosome. Other methods used have included -~
avoiding the use of autonomously replicating vector molecules and instead using techniques which favor integration of the introduced DNA into the host cell chromosome.
Methods of achieving integration of foreign DNA
into the host cell chromosome have included homologous recom-bination and illegitimate recombination. There are two ways of inserting DNA sequences into specific locations on a chrom-osome by homologous recombination: Campbell-type homologous -recombination and double reciprocal recombination, which are shown in Figures lA and lB, respectively. A third way of introducing DNA sequences into the chromosome, this method -using a two-step replacement mechanism, is shown in Figure lC. In principle, a Campbell-type recombination is used, but the final result is a chromosomal arrangement that contains no duplicated sequences, and thus no amplifiable unit, in the recombined part of the chromosome. It therefore resembles a double reciprocal recombination.
Apart from using homologous recombination for the ~-integration of foreign DNA into the chromosome it is also pos-sible to integrate DNA by illegitimate recombination. Inte-~- 30 grated vector molecul~es can be selected for under conditions which inhibit autonomous replication of non-integrated vector molecules. Use of illegitimate recombination for integration -is depicted in Figure lD. The absence of tandem duplications in the obtained chromosomal sequence arrangements make the pathways shown in Figures lB, C and D preferred for stable introduction of DNA sequences into the genome. Chromosomally integrated genes have included both homologous and heterolo- ~
, gous genes where the amplification of the chromosomally inte- -' ~. -- 6 _ 1 3 2 71 7a grated DNA has been in a tandem array. These chromosomally amplified sequences have been reported to be unstable al- ;
though stability has been reported in some cases. It is therefore desirable to develop methods whereby DNA integrated into the chromosome is stably maintained.

Relevant ~iterature Integration of exogenous DNA by homologous recombi-nation into the chromosome of Bacillus subtilis has been des-cribed by Duncan et al., Proc. Natl. Acad. Sci. USA 75 (1978) ~;
3664-3668 and for Anacvstis nidulans by Williams and Szalay, Gene ~ (1983) 37-51 and in International Patent Application WO 84/00381. Integration by homologous recombination of a -~
heterologous gene, which cannot be maintained stably when carried on a plasmid vector, into the chromosome of a micro- ~^
organism is described in EP-A-0127328. ~ ~
Amplification of chromosomally integrated genes, ;
both homologous and heterologous has been documented. See - -for example: Saito et al., Proceedings of the Fourth Inter-national Symposium on Genetics of Industrial Microorganisms, ~ --Kyoto, Japan, 1982, pp. 125-130; Young, J. Gen. Microbiol.
l~Q (1984) 1613-1621; Janniere et al.~ Gene 40 (1985) 47-55;
Sargent and Bennett, J. Bacteriol. 161 (1985) 589-595; Gut-terson and Koshland,~Proc. Natl. Acad. Sci. USA 80 (1983) 4894-4898; Hashiguchi et ~L., Agric. Biol. Chem. 49 (1985) 545-550; ~ilson and Morgan, J. Bacteriol. 163 (1985) 445-453; :
French Patent Publication No. 2,563i533 published october 31, -1985; and EP-A-0134048. Spontaneous amplification in pro-karyotic cells has been reported and can be selected for. ;
See for example the review by Anderson and Roth, Ann. Rev.
Microbiol. ~1 (1977) 473-505.
In all cases referred to above, amplification of chromosomally integrated DNA was in a tandem array. This type of chromosomal amplification sequence has been reported 35~ to be unstable, although rather good stability was found in some cases, as discussed by Janniere et al., Gene 40 (1985) 47-55.
Stabilization of naturally occurring amplified pro- -~
karyotic genes due to the presence of other essential genes between these ampIified sequences has been reported. For , . ~ : - ~

_ 7 _ 132717~
,, , example, of the 9 to 10 coples of the ribosomal RNA gene sets occurring in the B. subtilis chromosome, two tandemly located -~
sets were separated by a cluster of tRNA genes (Wawrousek and Hansen, J. Biol. Chem. 258 (1983) 291-298). In other cases, naturally occurring tandemly repeated ribosomal RNA operons were deleted, both in ~. coli and in B. subtilis, with little effect on the phenotypic properties of the organism: Ellwood and Momura, J. Bacteriol. 143 (1980) 1077-1080 and Loughney et al., J. Bacteriol. 154 (1983) 529-532, respectively.
Integration of plasmids into the chromosome of B.
subtilis by illegitimate recombination using the vector pE194 has been described bv Hofemeister ~ al., Mol. Gen. Genet.
189 (1983) 58-68 and Prorozov et ~1-, Gene 34 (1985) 39-46.
Several genes for extracellular enzymes of bacilli have been successfully cloned, such as the alpha-amylase genes of B. amvloliauefaciens (Palva et al., Gene 15 (1981) 43-51), B. licheniformis (Ortlepp, Gene 23 (1983) 267), B.
stearothermo~hilus (Mielenz et al., Proc. Acad. Sci. USA 80 ~-(1983) 5975-5979; EP-A-0057976) and B. subtills (Yang et al., Nucleic Acids Res. 11 (1983) 237); the levansucrase gene of B. subtilis (Gay et al., J. Bacteriol. 153 (1983) 1424); the neutral protease encoding genes of ~. stearothermo~hilus (Fuji Q~ ~1-, J. Bacteriol. 156 (1983) 8310, B. amYloliaue-faciens (Jonjo et ~L-, J. Biotech. 1 (1984) 165) and of B.
subtilis (Yang et ~1-, J. Bacteriol. 160 (1984) 115; the serine or alkaline protease encoding genes of B. subtilis 1 (Wong et ~1., Proc. Natl. Acad. Sci. USA ~1 (1984) 1184), B. ~ ~:
i licheniformis (Jacobs et al., Nucleic Acids Res. 13 ~1985) 8913) and B. amvloliauefaciens (Wells et al., Nucleic Acids Res. 11 (1983) 7911).
Protoplast transformation for several species of gram positive microorganisms has been reported. For B. subti-lis a protocol for protoplast transformation was described bY
Chang and Cohen (Mol. Gen. Genet. 168 (1979) 111-115), which ;
has been widely used. Similar successful protocols have been described for the transformation of B. meaaterium protoplasts (Vorobjeva et al., FEMS Microbiol. Letters 7 (1980) 261-263), --B. amvloliauefaciens protoplasts (Smith et al., Appl. and Env. Microbiol. 51 (1986) 634), B. thurinaiensis protoplasts (Flsher et al., Arch. Microbiol. 1~ (1981) 213-217), B.

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- 8 - 132717~
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s~haericus protoplasts (McDonald, J. Gen. Microbiol. 130 (1984) 203), and B. la~vae protoplasts (Bakhiet et al., Appl.
and Env. Microbiol. 49 (1985) 577); in the same publication unsuccessful results were reported for B. ~o~illae. The pro-tocol was successful for B. ~olvmvxa, ~. licheniformis, B.macerans and B. lateros~orus but not for B. coaaulans, ~.
cereus and B. Dumilus ~ even though good protoplast formation was observed (Mann et al., Current Microbiol. 13 (1986) 131-135). ~
Other methods of introducing DNA into protoplasts ~-include fusion with DNA containing liposomes (Holubova, Folia ~ -Microbiol. 30 (1985) 97), or protoplast fusion using a read-ily transformable organism as an lntermediate host cell (EP-A-0134048).
-SUMMARY OF THE I~ENTIoN

Prokaryotic host cells, and methods for their prepa-ration, are provided which comprise at least two copies of a -DNA sequence encoding a polypeptide of interest stably inte-grated into the host cell chromosome. Stable maintenance of -the exogenous DNA sequence is obtained by integrating two or more copies of the sequence into the host cell chromosome wherein the copies are separated by endogenous chromosomal -~
DNA sequences.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In accordance with the present invention, prokaryo-tic cells, and methods for their preparation, are provided in which two or more copies of a DNA sequence are stably integra- -ted into the chromosome. A host cell comprising a DNA sequ-ence encoding a polypeptide of interest is transformed with a DNA construct comprising said DNA sequence. Transformed cells ' ~5 in which the integrated DNA sequences are separated by endo-. genous chromosomal sequences from the gene to be amplified are then selected for. The endogenous intervening sequences r~
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9 1327~7~
are generally vital to the host cell. Loss of amplified se-quences by homologous recombination will be lethal to the host cell. Thus, there will be selection pressure for cells carrying the amplified sequences without the necessity for using antibiotics or like selection means. Integration may be achieved either by homologous recombinatlon or by illegiti-mate recombination. Techniques which can be used to obtain the desired cells are as shown in Figures 2A and 2B, respec-tively.
When homologous recombination is used, several -stretches of DNA sequences can be present in the vector mole-cules which are homologous to the host cell chromosome, es- -pecially when one or more copies of the gene to be amplified have already been introduced into the host cell. The vector molecule thus can include a DNA sequence of interest; a tar-get DNA sequence; and a marker DNA sequence.
Care has to be taken that only the desired recom-bined chromosomal arrangements are selected for. This can be achieved by using linear DNA molecules for recombination.
The circular vector molecule to be integrated is cut with a restriction enzyme in the region homologous to the target sequence. In this way recombination and integration at this ~-specific site can occur preferentially. In addition to being present in the vector molecule, the DNA sequence of interest can also be present in the host cell chromosome. The DNA se-quence may be a DNA sequence encoding any structural gene which it is desired to amplify. The DNA sequence may be en-dogenous to the host organism, or may have been inserted into the host chromosome in a previous transformation step.
Target sequences for non-tandem gene amplification will preferably be chosen from among non-essential genes, for example in the case of Bacilli as host organisms, the genes encoding extracellular enzymes or genes involved in sporula-tion can be used as target sequences. Integration of DNA
sequences in these genes will generally inactivate the gene.
~oss of expression of the gene can then be monitored and used for the selection of the desi-ed recombinant strains.
When illegitimate recombination is used for chro- -mosomal gene amplification as depicted in Figures lD and 2A, ~ ~:
-r , 1 -10- 132717a conditions for integration and selection are preferred in which homologous recombination does not predominate over illegitimate recombination. A preferred means of avoiding homologous recombination is to transform first and second 5 host cells which lack the structural gene of interest with a -~
vector comprising a DNA sequence encoding a polypeptide of interest, and a marker gene. First and second host cells in which the DNA sequence is present at different locations can ~
then be selected and combined under fusing conditions to :-yield a transformed cell with at least two copies of the DNA
sequence encoding the structural gene of interest at scat-tered locations in the second host genome. For ease of sel-ection the first host can be killed prior to fusion.
The gene(s) of interest may be any prokaryotic or eukaryotic gene. These genes may include bacterial genes, unicellular microorganism genes, mammalian genes, or the like. The structural genes may be prepared in a variety of ways, including synthesis, isolation from genomic DNA, pre-paration from cDNA, or combinations thereof. The various 20 techniques of manipulation of the genes are well-known, and -include restriction, digestion, resection, ligation, i~ vitro mutagenesis, primer repair, employing linkers and adapters, `
and the like. Thus, DNA sequences obtained from a host may - -~
be manipulated in a variety of ways, depending upon the re-quirements of the DNA construction. See Maniatis et ~1., Molecular Cloning, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 1982. :
The structural genes may express a variety of poly-peptides or proteins, such as enzymes, hormones, lymphokines, -surface proteins, blood proteins, structural proteins, immuno-globulins, or the like, from mammals, unicellular microorga-nisms, e.g., bacteria, fungi, such as yeast, or filamentous fungi, algae, protozoa, etc., plants or other DNA source. of particular interest are enzymes, more particularly proteases , 35 and amylases. Illustrative of such enzymes are serine and non-serine proteases, including high alkaline serine pro-teases, alpha- and beta-amylase, and the like. A preferred source for a serine protease is Bacillus novo species PB92, ~

":

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and for an alpha-amylase is B. licheniformis strain T5, as well as mutants and variants of these strains.
The gene that forms part of the suitable vector can be obtained by methods generally known in the art. Generally, the method comprises preparing a genomic library from the organism expressing a high alkaline protease. The genomic library is convenlently prepared for example by ligating DNA
fragments of the donor strain into a suitable vector.
By the term //suitable vector~ is meant a DNA con-struct comprising a structural gene encoding a protein ofpolypeptide of interest. The structural gene is joined in proper orientation to control regions such as a promoter se-quence, a sequence forming the ribosome binding site and se-quences controlling termination of transcription and transla-tion of the structural gene, which control regions are func-tional in the host cell. Where the host cell has transforma-tion and integration frequencies which are too low to permit direct selection for integration without intermediate isola-tion of plasmid containing cells, such as industrial Baci~lus strains, the vector can additionally comprise an origin of replication that is capable of replicating autonomously in the host cell.
Where the gene is obtained from a donor cell which has transcriptional and translational initiation and termina-tion regulatory signals which are recognized by the host pro-karyotic cell strain, it will usually be convenient to main-tain the original regulatory sequences of the structural gene.
In addition, the transcriptional initiation region may provide for constitutive or inducible expression, so that in appropri-ate situations, the host may be grown to high density beforehigh levels o~ expression of the structural genes of interest are obtained.
Where the structural gene is from a source whose regulatory signals are not recognized by the host cell, it will be necessary to obtain regulatory regions recognized by the host cell and to insert the structural gene between the initiation and termination regulatory signals. In some instances the exogenous structural gene with its own stop ~,J;
1'~

- 12 - 132717~ ~ -codon(s) may be inserted in reading frame behind the N-terminus codons of an endogenous structural gene which re-tains its natural regulatory signals.
It is desirable that the expression product be se-creted. Where the expression product is naturally secretedand the leader signals and processing signal(s) are recoynized by the host cell, this will entail no difficulty. However, where the product is not secreted because the host cell does not recognize the secretory leader signals and/or processing signal~s), or the signals are not functional to a satisfactory degree in the host cell, then it may be necessary to isolate or synthesize DNA sequences coding for the secretory leader ;~
signals and processing signal(s) of a host cell polypeptide and join them in proper reading frame to the 5~-end of the structural gene.
The vector may additionally include a marker gene ~
conferring resistance to an antibiotic to which the host ~ :
strain is sensitive. The marker gene, when used in chromo-somal integration of the vector, has to fulfil the demand that :
survival selection is possible even if only one or a few copies of the marker gene are present in the host strain. By marker is intended a structural gene capable of expression in a host, which provides for survival selection. By asurvival selection~ is intended imparting prototrophy to an auxotrophic - 25 host, biocide or viral resistance. For prototrophy, various genes may be employed, such as leu, his, trp, or the like.
For biocide resistance this may include resistance to antibio-tics, e.g., neo, cam, tet, tun, kan, or the like~ Other mar-kers include resistance to heavy metals, immunity, and the like. The various DNA sequences may be derived from diverse sources and joined together to provide for a vector which in-cludes one or more convenient, preferably unique, restriction ~ sites to allow for insertion or substitution of the structural ~-1, genes at such sites or in place of lost fragments to provide ~ 35 the plasmid construct.
¦ ~ Selection for chromosomal integration may be aided by using a plasmid with an origin replication having a muta-tion which makes its functioning temperature-sensitive in the , - ,~

3~

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host cell. See, for example, Ehrlich, Proc. Natl. Acad. Sci.
USA 75 (1978) 1433.
Once the plasmid construct has been prepared, it may now be cloned in an appropriate _loning host. Any host may be used which is convenient, is readily transformable, and allows for replication of the plasmid construct and transfer to the host cell. A large number of strains are available which have -a high efficiency of transformation and are usually auxotro- -phic and/or antibiotic sensitive. Where the host cell is an 10 industrial Bacillus strain, the use of the same organism as -the host cell for cloning of the plasmid construct has many advantages in that it permits the use of a single replication system as well as the same marker for survival selection in both the cloning host and the host strain. See, for example, European application EP-A-134048, which disclosure is incor-porated herein by reference.
The plasmid construct may be introduced into the cloning host in accordance with conventional techniques, such as transformation, employing calcium precipitated DNA, conju-gation, or other convenient technique. The cloning host maythen be grown in an appropriate nutrient medium, under selec-tive conditions to select for a host containing the plasmid ~ ;
construct. For auxotrophic hosts, the nutrient medium is de-ficient in the required nutrient, while for biocide resistance, e.g., antibiotic resistance, a cytotoxic amount of the bio-cide(s) is employed in the nutrient medium.
Various host cells may be employed. These include E. ~Qli, Bacillus strains, especially Bacillus subtilis, Pseu-domonas, and Streptomvces. In choosing a host cell, various factors are taken into account, including factors which can affect expression of the gene to be amplified and production of the desired product. ~hus it is desirable to use a host cell in which there is recognition of regulatory signals; ease of secretion; reduced degradation of the desired product, etc.
A preferred host cell already produces the polypeptide of in-terest, and may be either a wild type organism or a mutant or-ganism. The host cell can also be a mutant of an organism which produces the polypeptide of interest which itself, how-. . i:J
: 1;~
- . .

^` 1327175 ever, is non-producer. Where the polypeptide of interest is a protease or an amylase, preferred strains include ~cillus novo species PB92 and Bacillus licheniformis strain T5, respec-tively, as well as mutants and variants of these strains.
In addition, industrial strains may be employed which have the desired traits of an industrial strain. Ex-amples of strains which may be employed include strains used for the industrial production of enzymes such as: B. licheni-formis, B. amvloliquefaciens and alkalophilic Bacilli. The industrial strains are chosen from organisms which may be iso-lated in the soil or available from depositories or other :
sources or obtained by modification of such strains. The industrial strains are highly robust and stable. Furthermore, said strains are resistant to phage infection and to genetic ' exchange, that is introduction of DNA by conventional trans-formation procedures. The conventional industrial strains are also prototrophic, in order to avoid adding expensive amino acids to the nutrient medium. Other characteristics of indus-trial strains are their high productivity until the end of the ~-fermentation, which can be as long as a week, stable cell con-centration upon exhaustion of the broth, and high productiv- -- ity, usually at least 5 g/l (0.5% w/v) of a specific secreted -protein.
Transformants can be obtained having genes either in tandem arrangement or scattered in the chromosome. In gener-al, it is possible to select transformants containing scat-tered genes from mixtures of the two types of transformants mentioned, by isolating chromosomal DNA of each individual ;
transformant, subsequently analyzing said DNA with respect to the relative locations of said genes by, for example, the method of Southern, J. Mol. Biol. 98 (1975) 503-517 or other means known to those skilled in the art, thereby identifying scattered integration of said genes.
Means for obtaining scattered gene transformants avoiding tandem integration include r using double reciprocal recombination as illustrated in the Figure lB and 2B, the use ~;~ of linearized DNA constructs comprising the DNA sequence to be ,;~ , ' . ~
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amplified, a marker gene and target sequences for recombin-ation.
Furthermore, specific means for obtaining scattered gene transformants include the use of illegitimate recombina-tion as illustrated in Figure 2A, in which isolation of tandem transformants can be avoided by selection, using differential expression of a marker gene, for example a gene encoding anti- --biotic resistance, where sensitivity to the antibiotic is dif-ferent in strains with tandem integration of the gene as op-posed to non-tandem integration. Generally, the length of the intervening endogenous DNA sequences will be less than 10 kbp.
Additionally, means for obtaining scattered g~ne ;~
transformants avoiding tandem duplication include the use of killed protoplasts of a homologous donor strain carrying a DNA
construct comprising the structural gene and a marker gene, the structural gene being integrated in the chromosomal at a dif-ferent location with respect to the acceptor strain. -Transformation of the host cells preferably involves the use of protoplasts prepared from the host strain. Proto- -~
plasts generally are prepared from the cells in accordance with conventional ways, e.g. lysozyme or zymolyase treatment, and the protoplasts carefully suspended in an appropriate medium having proper osmolalities for maintaining the integrity of the protoplast. For industrial Bacillus strains, methods for pre-paring protoplasts are described in EP-A-0134048, published on March 13, 1985. Where the host strain is an alkalophilic Bacillus strain, protoplasts may conveniently be prepared at alkaline pH, preferably about pH 8Ø This procedure is dis-closed in Canadian Patent Application No. 560,126 filed February 29, 1988.
The host cell can be transformed by combining the plasmid construct or a cloning host protoplast with the host cell protoplast in the presence of an appropriate fusogen. Any fusogen may be employed which provides the desired degree of efficiency, for the most part polyethyIene glycol is found to ~-provide high efficiency of fusion with great convenience.
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After a short time, the fusogen mixture is replaced with an appropriate nutrient medium and cells regenerated in a selec-tive medium, conveniently by plating on an agar plate.
Transformants obtained by combining a host cell with a suitable DNA construct can contain said DNA construct or part thereof either directly as an integral part of their chromosome or as free vector molecules when the DNA constructs contain an origin of replication functional in said host cell.
A means of selecting for transformants wherein the 10 DNA construct is integrated into the chromosome is to use a ~ -~
plasmid containing a temperature-sensltive origin of replica-tion. Transformants are grown in a selective medium at the permissive temperature, then shifted to a non-permissive tem-perature. Coloniés expressing the marker gene at the non- - `
permissive temperature are then isolated and cultured in sel-ective medium at the permissive temperature. Plasmid absence -can be verified, for example, by isolating total DNA from the colonies and electrophoresising on an agarose gel or by dem-onstrating lack of ability of the transformants to transform competent cells. Determination of the way in which integra-tion into the chromosome has taken place can be analysis of -the chromosomal DNA by, for example, the method of Southern, J. Mol. Biol. 98 (1975) 503-517 or other means known to those skilled in the art.
When there is a differential sensitivity to the selective agent between transformants containing additional copies of the marker gene in a tandem array as compared to those in which the marker gene is incorporated at scattered locations in the host genome, transformants can conveniently be grown in medium containing the appropriate concentration of selective agent to select for transformants with non-tandem integration.
Another means of obtaining transformants with scattered integration of copies of the DNA sequence of inter-est is to use a protoplast prepared from a homologous donorcell, containing at least one copy of the DNA sequence of interest at a location on its chromosome different from that of the recipient host cell. The homologous donor cell can i~ "
, - 132717~

be prepared, for example, by transforming a cell which does not contain the structural gene of interest with a vector comprising the structural gene. Integration of the DNA se-quence into the donor cell chromosome can be facilitated by using a plasmid containing a temperature-sensitive origin of replication and growing transformants under selective condi-tions first at the permissive temperature and then at the non-permissive temperature as described above, then isolating colonies expressing the marker gene.
Following verification of the absence of plasmid DNA, the chromosomal DNA can be isolated and analyzed accord-ing to the method of Southern, suDra, by hybridizing with a probe labeled with, for example, 32p or biotinylated nucleo-tides. The probe may be CDNA encoding the polypeptide of in-terest or fragments thereof as well as DNA constructs or frag-ments thereof comprising the DNA sequence of interest, for ex-ample a vector. Transformants containing the gene of interest at an alternate location as compared to that of the gene donor -strain can then be used as an homologous donor cell. The re- :
cipient strain host is preferably the same as the strain used as the source of the DNA sequence of interest, or a strain in which the DNA sequence of interest is located at a different region of the chromosome than in the transformed donor cell.
To aid in selection, the donor cell preferably is killed with a cytotoxic agent prior to or during protoplast formation. Various agent may be employed to kill the donor cell, including antibiotics, but iodoacetamide is found to be convenient, efficient, and does not interfere with the subse- -quent fusion. When dead cloning host protoplasts are used, the ratio of dead protoplast to the acceptor strain host will be preferably at least about 1:1 and an excess of the dead protoplast may be employed. - ~
Following fusion of the dead donor cell protoplast :
and the recipient host cell protoplast, transformants can be selected by means of the marker gene. DNA can then be iso-lated and analyzed as described above to identify transform-ants in which more than one copy of the gene of interest has -~
.:
:
~ri .:.. :
, - 18 - 132717~
been incorporated into the genome and are separated by endo-genous chromosomal sequences. ;
Scattered two-gene transformants are then screened in appropriate ways for detection of increased expression of the polypeptide of interest. Various techniques may be em-ployed, particularly where enzymes are involved which have well established methods of detection. Alternatively, where enzymes are not involved or there is no available detection system, bioassays, antibodies, or DNA or RNA hybridization can be employed for screening the clones to determine the presence of the plasmid construct and expression of the structural gene of interest.
The host cell containing the chromosomally inte- ~-grated plasmid constructs or fragments thereof is then grown in a nutrient medium under conventional fermenting conditions.
The fermenting may be continued until the broth is exhausted.
Where the product has been secreted, the product may be iso-lated from the broth by conventional techniques, e.g., extrac- -tion, chromatography, electrophoresis, or the like. Where the -product is retained in the cytoplasm, the cells may be har-vested by centrifugation, filtration, etc., lysed by mechani-cal shearing detergent, lysozome, or other techniques and the product isolated as described previously. By employing the subject method, stable integration of at least two copies of a DNA sequence can be achieved as a means of gene amplification.
The following examples are offered by way of illus-tration and not by way of limitation.

.
3 ;
- ' ~

~ .

- 19 132717~ :

Expression of the PB92 Serine Protease Gene - .' Bacillus subtilis lA40 containing pM58 was grown in minimal medium (Spizizen et al., Proc. Natl. Acad. Sci. USA 44 (1958) 1072-1078) to which had been added 0.02% casamino acids 50 ~g/ml tryptophan, 20 ~g/ml methionine, 20 ~g/ml lysine and 20 ~g/ml neomycin. After 24 hours, the culture was centrifuged 10 and the supernatant assayed for protease activity using dime- -thyl casein as substrate (Lin et al., J. Biol. Chem. 244 (1969) 789-793. A culture of ~. subtilis lA40 containing the plasmid pUBllO used as a control showed less than 1/60 of the protease~
activity shown by the pM58 transformed culture. Protease ac-tivity was completely inhibited by treatment with 1 mM phenyl-sulfonyl fluoride (PMSF), but not by treatment with 20 mM EDTA.
Aliquots of the above described supernatants were analyzed on protein gel according to the method of ~aemmli, - Nature 227 (1970) 680. Samples for analysis on these gels were .
20 prepared by treatment of the supernatants with 5% trichloro- ; :
acetic acid (TCAj. Following centrifugation of the sample the -~
pellet of precipitated protein was washed twice with acetone -~ then dissolved in 40 ~1 sample buffer (0.5 M Tris/HCl pH 7.5,~
~` 10% v/v 2-mercaptoethanol, 50% v/v glycerol and 0.05% Bromo- :~
phenol Blue) by boiling for 10 minutes. After electrophoresis, the gels were stained using Coomassie Brilliant Blue. Culture supernatant samples were then analyzed by electrophoresis. -Three different ~ btilis lA40 strains were used: a strain containing pUBllO; or pM58; or no plasmid; and Bacillus PB92 30 protease as a control. After electrophoresis, the gels were ' stained using Coomassie Brilliant Blue and destained. The sample from B. subtilis strain lA40 containing pM58 contained a 31 kD protein, which comigrates with Bacillus Ps92 protease.
This protein was not detected on the control lane of strain B.
,.. ~ ,. .
subtilis lA40 containing pUBllO.
All serine proteases have similar molecular weights. -The cloned serine protease of Bacillus PB92 therefore was dif-~`' ~: ' ' -.';'.,' 132717~

ferentiated from known serine proteases (B. subtllis subtili-sin, Carlsbera subtilisin), by transformation of pM58 and pUsllO to the protease negative B. subtilis strain DB104 (R.
Doi, J. Bacteriol. l~Q (1984) 442-444) and analysis of the extracellular proteases produced. The obtained transform-ants were grown in minimal medium (Spizizen et al., su~ra) containing 0.02% casamino acids, 50 ~g/ml histidine and 20 ~g/ml neomycin. After 24 hours, samples were taken, centri-fuged and without pretreatment analyzed on histidine/MOPS
gels containing 75 mM KOH, 40 mM histidine, 100 mM MOPS (3-(N-morpholino)-propanesulfonic acid), pH 7.5 and 5% polyac-rylamide. Electrophoresis buffer contained 40 mM histidine, 100 mM MOPS, pH 6.6. Samples were run in the direction of the cathode. Protease bands were detected with Agfa Pan 100 -Professional films (Zuidweg ~ al., Biotechnol. and Bioengin.
1~ (1972) 685-714j. These results are shown in Figure 3. As shown in Figure 4, pM58 harbours the gene encoding Bacillus PB92 protease.
:
EXAMP~E 2 .
~çquencina of the Bacillus PB92 Serine Protease Gene -The entire sequence of a ~lI-EeaI fragment of pM58 was determined by the method of F. Sanger, Proc. Natl. Acad.
Sci. USA 74 (1977? 64630 Restriction fragments of pM58 (see - Figure 4) were cloned in phage M13 vectors mplO, mpll and ~-mpl8 (Messing Q~ al., Nucleic Acids Res. 9 (1981) 309-321).
Insertions of pM58 fragments were screened by plaque hybrid- ~ -~-~ ization. After sequencing, ten oligonucleotides located at regular distances on the gene were made and sequencing was -~ repeated, confirming the sequence shown in Figure 5.

- 21 - 132717a :

Construction of Serine Protease Containina Plasmld ~MAX-4 To construct plasmid pUCN710 (Figure 6A) pUBllO was digested with ~lgI and ~y~II. The fragment containing the gene conferring neomycin resistance was purified on low melt-ing agarose and made blunt with Klenow polymerase and NTP~s (Maniatis, Molecuiar Cloning: A Laboratory Manual. Cold Spring Harbor 1982). Plasmid pUC7 !Vieira et ~1., Gene 19 (1982) 259-268) was linearized with ~alI and made blunt as described above. Both fragments were ligated with T4 ligase (Maniatis) and transformed to E. ~Qli JM103. Selection took place on 2xTY plates (1.6% w/v Bacto-trypton, 1% w/v yeast extract, 0.5~ NaCl) containing 50 ~g/ml ampicillin and 10 ~g/ml neomycin. The resulting plasmid, named pUCN710, was digested with ~mHI. The plasmid pE194 (Jordanescu, Plasmid :
1 (1978) 468-479) was digested with BclI. The fragments from both digestions were ligated with T4 ligase and transformed to ~. S~btilis lA40. Selection took place on minimal plates ~
containing 20 ~g/ml neomycin (see Example 1). The plasmid ob- - -tained, pE194-neo (Figure 6A) contains the neomycin gene and a temperature sensitive origin of replication. -;~ 25 Subcloning of the protease gene in integration vec- -tor pE194-neo was performed as follows: pM58 (see Example 1) -was digested with ~aI and E~lI and ~glII. Plasmid pE194-neo was digested with ~aI. These fragments were ligated with T4 ligase and transformed to ~. subtilis lA40. Transformants were selected based upon neomycin resistance and an increase - in protease production, as judged by casein cleavage products -~ precipitation (halo formation, see Example 1). Plasmid pMAX-4 was obtained, the structure of which was confirmed by res-tri-ction enzyme analysis (see Figure 6B). -' , :

:~ "''" ' .' ~, ; ' ' - 22 - 132717~ :

Proto~last Transformation of Bacillus Strain PB92 by DMAX-4 Bacillus strain Psg2 was grown overnight in 100 ml NBSG-X medium (Thorne et al., J. Bacteriol. 91 (1966) 1012-1020). The culture was centrifuged for 10 minutes at 4,500 rpm in a Sorvall model GSA rotor. Protoplasts were prepared by incubating the Bacilli for one hour at 37C in l0 ml Alka-lic Holding Medium (A~M) containing 0.5 M sucrose, 0.02 M
MgC12 and 0.02 M Tris/maleate, pH 8,0, in sterile water to which 0.4 mg/ml lysozyme was added. The protoplasts were pel- ~ ;
leted (10 minutes at 4,500 rpm), resuspended in 5 ml AHM+ pH
8.0 buffer (AHM buffer to which 3.5% w/v Bacto Penassay Broth and 0.04% w/v Albumine Merieux had been added) mixed, then re- -~
- pelleted as above. After being resuspended in 5.0 ml of alka- ~
line holding medium, 0.5 ml of this~suspension of protoplasts ~-were mixed with 5 ~g of demineralized water containing l~g of plasmid DNA and incubated for 2 minutes in the presence of 30% w/v polyethylene glycol 8,000, pH 8Ø After 1:3 dilu- ~
tion with AHM+ pH 8.0 medium and centrifugation, the pellet ~ -was resuspended in a small volume (1 ml) of AHM+ and incu~
bated for 2-3 hours. One hundred microliter aliquots were -~
25 plated on freshly prepared regeneration plates containing 0.5 - -M Na succinate/HCl pH 8.0, 1.5~ wiv agar, 0.5~ w/v casamino -~ acids, 0.5% w/v yeast extract, 0.031 M phosphate buffer pH -8.0, 0.5% w/v glucose, 0.02 M MgC12 and 0.02% w/v Albumine Merieux. These plates also contained 1000 ~g/ml neomycin for selection. After incubation at 37C for at least 72 hrs., the colonies were replica-plated onto heart infusion agar platés containing 20 ~g/ml neomycin. -Intearation of pMAX-4 in the ~-Bacillus Strain PB92 Chromosome ,~: . . .

- 132717~ ~

A transformant of Bacillus PB92, containing plasmid pMAX-4, was incubated in Tryptone Soya sroth (Tss) contalning either 1 ~g/ml or 20 ~g/ml neomycin for 24 hrs. at 37C. Two ml portions of the cell suspensions were then diluted in 100 ml of TSB containing 1 ~g/ml or 20 ~g/ml neomycin, respective-ly, and incubated for 24 hrs. at 50C. After 24 hrs. 5 ml samples of both cultures were diluted again, as described ab- :ove, and incubated for 24 hrs. at 50~C, again in the presence of 1 ~g/ml or 20 ~g/ml neomycin, respectively. The last pro-cedure was repeated once more. The cell suspensions were then diluted 100-fold and plated on Heart Infusion (HI) agar plates containing 1 ~g/ml neomycin for the samples from the flasks ;-containing 1 ~g/ml neomycin, and 20 ~g/ml neomycin for the ~
samples from the flasks containing 20 ~g/ml neomycin. The -plates were incubated for 16 hrs. at 50C. Neomycin-re-sistant colonies were isolated and cultured in 10 ml TSB med- ~
ium containing 1 ~g/ml neomycin for 16 h at 37C. From these ;
cultures total DNA was isolated (Holmes et al., Anal. Biochem. - -114 (1981) 193-197). Plasmid absence was verified by DNA elec-trophoresis on agarose gel. Absence of plasmid DNA from sam-ples in which plasmid DNA was not detectable was confirmed by ~
transformation of total DNA to B. subtilis lA40. Samples --lacking the ability to transform ~. subtilis lA40 were con- ~
sidered plasmid-free. -~ ~-To check whether and in what way integration of ~ -~
pMAX-4 in the chromosome took place, chromosomal DNA was iso- ~
lated, digested with ~in~III, run on 0.5% DNA agarose gels and -blotted to nitrocellulose (Southern, J. Mol. Biol. 98 (1975) 503-517), and hybridized with 32p labeled nick-translated pM58 (Maniatis, 1982). The result of this analysis is shown in Fig- ;
ure 7A.
;~ Selection at 1 ~g/ml neomycin resulted in protease ;-genes tandemly located in the chromosome and separated by -plasmid sequences (strain PBT109) as a result of homologous ~; 35 recombination (Campbell-type mechanism). In an accumulation -i- of 30 independentiy isolated integrants, selection was per- : :
~ formed at 1 ~g/ml neomycin. One integrant was isolated which '~ contained the plasmid pMAX-4 on a random location in the :-: : .. .
,~ ~S~

.': ' - 24 - 1 3 2 7 1 7 ~ -chromosome as a result of an illegitimate recombination (strain PsT122). Selection at 20 ~g/ml neomycin resulted in a copy of plasmid pMAX-4 on a random location in the chromosome as a result of an illegitimate type of recombination. The lat-ter strain was named PBT108. The genetic organization of thestrains PsT109 and 108 are depicted in Figures 7s and 7C, re-spectively. Chromosomal analysis showed that integration in PBT122 and PBT108 occurred on different locations in the chro-mosome.

Stabilitv of the Du~licated Protease Genes in Strains PBT108 and PBT109 -One hundred ml of production medium (containing:
1% starch, 4% lactose, 0.87% K2HPO4, 0.5% yeast extract, 0.5%
(NH4)2HPO4, 0.2% Tri Na citrate.2H2O, 0.05% MgSO4.7H2O, 0.07%
CaC12, 0.068% FeSO4.7H2O and antifoam 1 ml/l) without neomycin was inoculated with 0.2 ml of an overnight TSB culture (37C) of strain PBT108 or PBT109 in 500 ml shake flasks. After in-cubation for 44 hrs. at 37C under constant aeration the cul-ture was tested for neomycin-resistant colonies and for pro-tease activity.
Both strains PBT108 and PBT109 were also tested in -Eschweiler fermenters containing said medium to check the effect of upscaling to 10 1. The results of the fermentation experiments are summarized in the following Table 1.
.
Table 1 :
.
_ . :~ ' Strain Relative Production Percent of Neomycin-of Protease*Resistant Cells After Fermentation _ , , ., . . _ ......... , Control (PB92)100% _ " 7 PBT108 120% 100%
PBT109 115-120% 75-97%
.

'~ -~ 25 - 1~27175 * Protease activity was assayed using dimethylcasein as sub-strate as described by L,in ~ al., J. Biol. Chem. 244 (1969) 789-793.

Analysis of colonies derived from the Eschweiler fer-mentation of PBT109 after 2 days of culturing, showed that 3 25% of these colonies produced at the level of a strain con-taining only a single protease gene. These same colonies were found neomycin-sensitive due to excision of the pMAX-4 se- ~
10 quence by homologous recombination. However, analysis of the ~ -colonies derived from the strain PBT108 fermentation experi-ment showed that these cells were all neomycin-resistant. One ;;;
hundred of these neomycin-resistant colonies were taken at random and individually tested for protease production poten-15 tial, to determine whether they contained one or two produc- -~
tive protease genes. All 100 individually tested colonies .
produced at the level of a strain containing two genes, show- ~
ing that the two randomly integrated protease genes in PBT108 -:
are stably maintained under the fermentation conditions used. `'!''~'~`
EXAMPLE 7 ;

Construction of Inteqration Vector pElatB
'~ ' ' -'.' Plasmid pGB34, described in EP-A-0 134 048, was di-gested with the restriction enzymes BclI, ~gLI and ~glII. The restriction fragments obtained were blunt-ended with Klenow polymerase, then were ligated into the H~aI site of pE194-neo (see Example 6). Plasmid pE194-neo DNA was isolated as des-cribed by Birnboim and Doly (Nucl. Acids. Res. 1 (1979) 1513- :
1523).
The ligation mixture was transformed into B. sub-tili~ lA40, according to the method of Spizizen et ~1. (J..-Bacteriol. ~1 (1961) 741-746) using 0.5-1 ~g DNA per ml of competent cells. Cells from the transformation mixture were plated on minimal plates containing 2.8% K2HPO4, 1.2% KH2PO4, 0.4% (NH4)2SO4, 0.2% Tri Na citrate.2H2Q, 0.04% MgSO4.7H2O, - 26 - 1327i7~ .
0.00005% MnSO4.4H2O, 0.4% glutamic acid, 0.5% glucose, 0.02%
casamino acids, 50 ~g/ml tryptophan, 20 ~g/ml methionine, 20 ~g/ml lysine, 20 ~g/ml neomycin, 0.4% casein, 0.5% starch and 1.5% agar.
DNA of alpha-amylase producing colonies was iso- -lated as described by sirnboim and Doly and checked with re~
striction enzymes. From one of these transformants plasmid pElatB, see Figure 8, was isolated.

Transformation of the Alpha-Amvlase Neaative Strain Bacillus licheniformis T9 with pELa~@
: . .
Transformation of a~llus licheniformis strain T9 .. ..
was carried out as described in EP-A-0 253 455 with the ex-ception that the entire procedure was performed at 30C in-stead of 37C. Selection for transformants was carried out on minimal plates containing 20 ~g/ml neomycin. All trans-formants produced amylase. Restriction enzyme analysis per-` formed on DNA prepared as described by Birnboim and Doly showed that the transformants all contained pElatB.
. .
:.-:: .
EXAMPLE 9 ;~

In~eqration of DElatB into the B. licheniformis T9 chromosome :

Bacillus licheniformis strain T9 containing plasmid pElatB, was inoculated in Tryptone Soya Broth (TSB) containing ~-~ - 20 ~g/ml neomycin and incubated for 16 hours at 30C. A 5 ml portion of the ceil suspension was diluted in 100 ml of the same medium and incubated at 50C for 24 hours.
This procedure was repeated once. The cell sus-pension was then diluted 100-fold and plated on Heart Infu-3~ sion Agar plates containing 10 ~giml neomycin. After 40 ; hours of incubation at 50C, neomycin-resistant colonies were solated and cultured in 10 ml TSB medium, containing 10 ~g/ml 3~

1327175 ~

neomycin, for 16 hours at 30 C. Total DNA from these cultures was isolated (Holmes et al., Anal. Biochem. 114 (1981) 193-197). The absence of plasmids in these cells was verified by ~ ;~
DNA electrophoresis on agarose gels. Samples in which low molecular weight DNA was virtually absent, were rechecked onthe presence of plasmid DNA by DNA transformation to B.
subtilis l-A40 (Spizizen et al., 1961). Samples lacklng the :-~
ability to transform B. subtilis l-A40 to neomycin resistance `~
were considered plasmid minus.
To check whether integration of pElatB took place and ~
how it took place, chromosomal DNA was isolated from the trans- -formants (Saito-Minwa, Biochem. Biophys. Acta 72 (1963) 619-632), digested with EcoRI fractionated on 0.5% agarose gels, ~-blotted onto nitro-cellulose (Southern, J. Mol. Biol. 98 (1975) 503-517) and hybridized with 32p labelled nick-translated pGB33 -:
(see EP-A-0134048). The results from this analysis are shown -in Figure 9A. The data show that illegitimate recombination of pElatB took place resulting in a strain containing a single amylase gene on a different locus of the genome as compared with the original Bacillus licheniformis T5 amylase strain.
The strain obtained containing pElatB was named TB13. -., Construction of Strain T13F Containing Two Amylase ; - -Genes Separated by Endogenous Chromosomal Sequences .
In order to develop a strain containing two amylase genes separated by endogenous chromosomal DNA sequences, a fusion experiment was performed between Bacillus lichenifor-mls strain T5 (the original amylase gene containing amylase strain, see EP-A-0134048) and strain TB13 (the randomly in-tegrated, amylase gene containing strain). Protoplast fusion was performed as described in EP-A-0134048. Strain TB13 was killed with iodoacetamide prior to protoplast formation. -Strain T5 (neomycin sensitive) was not killed. Selection for . .
c~
,:

` - 28 - 132717~ :~
fusants took place on the regeneration plates containing 10 ~g/ml neomycin.
To check and identify potential fusants, chromo-somal DNA was isolated, digested with EcoRI, fractionated on 0.5% agarose gels, blotted to nitrocellulose filters (Southern, J. Mol. siol. 98 (1975) 503-517) and hybridized with 32p labeled nick-translated pGs33 (see EP-A-0 134 048).
The result of this analysis is shown in Figure 9B. One of the obtained fusants, T13E, contained two amylase genes separated by endogenous chromosomal sequences.

Stability of the duplicated amvlase aenes ~ -in strains T390 and T13F
:
The stability of strain T13F, a strain containing two chromosomal amylase genes separated by essential chromo- -~
somal sequences, was compared with that of strain T390, a strain with two chromosomal amylase genes located in a tandem array. Preparation of strain T390 is disclosed in EP-A-134048 (page 17, Table I), where it was referred to as B.
.licheniformis T5 (pGB33). Strains T13F and T390 were tested under fermentation conditions, namely 0.2 ml of an overnight 25 TSB culture (37C) was inoculated in 500 ml shake flasks -containing 100 ml production medium (see Example 7; after sterilization the pH was adjusted to 6.9 with NaOH) without neomycin. After incubation for 6 days at 40C under constant aeration the culture was tested for neomycin-resistant col-onies and amylase activity. The results of the fermentation experiment~ are summarized in the following Table 2. --,"
': .
.:
- rS
~. 1~

- 29 - 132717~ ~
Table 2 ~ ~
""'~ ' .':
.:' Strain Relative Amylase Percent of Neomycin-ResiStant ActivityCells After Fermentation* ~

T5 100% ~ ;~ :
Tsl3 20% 100% - --T13F 120% 100% -T3 9 0 200% 88~ ;
''.' ",' * More than thousand colonies were tested per strain. ~ ~
S , :
To exclude the possibility of excision of one amyl- ~ -ase gene without concomitant loss of the neomycin gene in strain T13F, 20 colonies derived from T13F fermentation were analyzed. Chromosomal DNA from 20 randomly chosen colonies ~; :
10 was isolated and characterized by hybridization experiments `
as described above. The results of 9 of these analyses are shown in Figure 10. All strains tested contained two amylase -~-genes, as demonstrated by the presence of two alpha-amylase genes containing E~QRI fragments in their chromosomal DNA.
In contrast to the genetic stability of strain T13F, strain T390 was found to be unstable upon fermentation resulting in 12% neomycin-sensitive colonies. One of these colonies was analyzed and found to contain only one alpha-amylase gene (Figure 10, lane 4). This shows that randomly integrated amylase genes are more stable than tandemly in-tegrated genes, under fermentation conditions.
It is evident from the above results that a pro-karyotic cell may be obtained in which stable gene amplifi-cation is achieved by selecting for transformed cells in ;;~
which non-tandem integration of at least two copies of the structural gene to be amplified has occurred. Integration may occur by homologous recombination or illegitimate recom-bination.
All publications and patent applications mentioned -i~ this specification are indicative of the level of skill of 132717a those skilled in the art to which this invention pertains.
The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without depart-ing from the spirit or scope of the appended claims.

, ' - .

' .~' ~

'. .' , ' '., -1' ' :

Claims (69)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A transformed prokaryotic host cell comprising at least two copies of a DNA sequence in its chromosome, said DNA sequence encoding a polypeptide of interest, wherein said copies are separated by endogenous chromosomal DNA which is vital to the host cell.

2. A transformed prokaryotic host cell comprising at least two copies of a DNA sequence encoding a polypeptide of interest, wherein said copies are separated by endogenous chromosomal DNA which is vital to the host cell, said cell being produced by the method comprising:
combining a recipient host cell comprising at least one copy of said DNA sequence integrated into its chromosome with (a) a DNA construct, comprising at least one copy of said DNA sequence and at least one of a marker gene and a temperature-sensitive origin of replication or (b) a donor host cell comprising said DNA construct, under transforming conditions;
selecting for a transformant wherein said DNA con-struct is integrated into the chromosome of said transfor-mant; and isolating from among said transformants, trans-formed prokaryotic host cells comprising at least two copies of said DNA sequence separated by endogenous DNA sequences which are vital to the host cell.

3. A transformed prokaryotic host cell according to Claim 1 or 2, wherein said prokaryotic cell is a Bacillus strain.

4. A transformed prokaryotic host cell according to Claim 3, wherein said Bacillus strain is an alkalophilic Bacillus strain or a Bacillus licheniformis host strain.

5. A transformed prokaryotic host cell according to Claim 4, wherein said alkalophilic Bacillus strain is Bacillus novo species PB92 or a mutant or variant thereof.

6. A transformed prokaryotic host cell according to Claim 4, wherein said Bacillus licheniformis host strain is Bacillus licheniformis strain T5 or a mutant or a variant thereof.

7. A transformed prokaryotic host cell according to Claim 1 or 2, wherein said polypeptide of interest is an enzyme.

8. A transformed prokaryotic host cell according to Claim 7, wherein said enzyme is a proteolytic enzyme or an amylolytic enzyme.

9. A transformed prokaryotic host cell according to Claim 8, wherein said proteolytic enzyme is a serine pro-tease.

10. A transformed prokaryotic host cell according to Claim 9, wherein said serine protease comprises substant-ially the following amino acid sequence:

.

11. A transformed prokaryotic host cell according to Claim 8, wherein said amylolytic enzyme is alpha-amylase.

12. A transformed prokaryotic host cell according to Claim 1 or 2, wherein the genome of Bacillus novo species PB92 or a mutant or variant thereof comprises said DNA se-quence.

13. A transformed prokaryotic host cell according to Claim 1 or 2, wherein the genome of Bacillus licheniformis strain T5 or a mutant or a variant thereof comprises said DNA
sequence.

14. A method for preparing a transformed prokary-otic host cell comprising at least two copies of a DNA se-quence encoding a polypeptide of interest, wherein said copies are separated by endogenous chromosomal DNA which is vital to the host cell, said method comprising:
combining a recipient host cell comprising at least one copy of said DNA sequence integrated into its chromosome with (a) a DNA construct, comprising at least one copy of said DNA sequence and at least one of a marker gene and a temperature-sensitive origin of replication or (b) a donor host cell comprising said DNA construct, under transforming conditions;
selecting for a transformant wherein said DNA con-struct is integrated into the chromosome of said transform-ant; and isolating from among said transformants, trans-formed prokaryotic host cells comprising at least two copies of said DNA sequence separated by endogenous DNA which is vital to the host cell.

15. A method according to Claim 14, wherein said selecting comprises:
growing said transformant comprising a DNA con-struct comprising a marker gene in the presence of a biocide to which said marker gene provides resistance; and identifying and isolating from said transformants, plasmid free transformants.

16. A method according to Claim 14, wherein said selecting comprises:
growing said transformant comprising a DNA con-struct comprising a marker gene and a temperature-sensitive origin of replication in the presence of a biocide at a non-permissive temperature; and selecting from said transformants, plasmid free transformants.

17. A method according to Claim 14, wherein said isolating comprises:
isolating chromosomal DNA from said transformants;
and hybridizing said chromosomal DNA with a labelled probe comprising said DNA construct or a fragment thereof whereby said transformed prokaryotic host cells are selected by detecting said label.

18. A method according to Claim 14, wherein said donor host cell is obtained by a method comprising:
combining a prokaryotic cell lacking a DNA sequence encoding said polypeptide of interest with said DNA construct under fusing conditions;
isolating transformed cells;
growing said transformed cells at a non-permissive temperature; and identifying and isolating transformed cells wherein said DNA construct is integrated into a location on the chromosome other than that in said recipient host cell.

19. A method according to Claim 14, wherein said prokaryotic cell is a Bacillus.

20. A method according to Claim 15, wherein said prokaryotic cell is a Bacillus.

21. A method according to Claim 16, wherein said prokaryotic cell is a Bacillus.

22. A method according to Claim 17, wherein said prokaryotic cell is a Bacillus.

23. A method according to Claim 18, wherein said prokaryotic cell is a Bacillus.

24. A method according to Claim 19, wherein said Bacillus is an alkalophilic Bacillus strain or a B. licheni formis strain.

25. A method according to Claim 20, wherein said Bacillus is an alkalophilic Bacillus strain or a B. licheni-formis strain.

26. A method according to Claim 21, wherein said Bacillus is an alkalophilic Bacillus strain or a B. licheni-formis strain.

27. A method according to Claim 22, wherein said Bacillus is an alkalophilic Bacillus strain or a B. licheni-formis strain.

28. A method according to Claim 23, wherein said Bacillus is an alkalophilic Bacillus strain or a B. licheni-formis strain

29. A method according to Claim 24, wherein said alkalophilic Bacillus strain is Bacillus novo species PB92 and said B. licheniformis strain is B. licheniformis strain T5.

30. A method according to Claim 25, wherein said alkalophilic Bacillus strain is Bacillus novo species PB92 and said B. licheniformis strain is B. licheniformis strain T5.

31. A method according to Claim 26, wherein said alkalophilic Bacillus strain is Bacillus novo species PB92 and said B. licheniformis strain is B. licheniformis strain T5.

32. A method according to Claim 27, wherein said alkalophilic Bacillus strain is Bacillus novo species PB92 and said B. licheniformis strain is B. licheniformis strain T5.

33. A method according to Claim 28, wherein said alkalophilic Bacillus strain is Bacillus novo species PB92 and said B. licheniformis strain is B. licheniformis strain T5.

34. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said polypeptide of interest is an enzyme.

35. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said polypeptide of interest is an enzyme and said enzyme is a serine protease or an amylase.

36. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said polypeptide of interest is an enzyme and said enzyme is a serine protease or an amylase and said serine protease has at least 70% homology in nucleotide sequence with a proteolytic enzyme encoding gene from Bacillus novo species PB92.

37. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said polypeptide of interest is an enzyme, said enzyme is a serine protease and said serine protease has substan-tially the following amino acid sequence:

.

38. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said polypeptide of interest is an enzyme, said enzyme is a serine protease, said serine protease has at least 70%
homology in nucleotide sequence with a proteolytic enzyme encoding gene from Bacillus novo species PB92 and said serine protease has substantially the following amino acid sequence:

.

39. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said DNA construct is pMAX-4 or pElatB.

40. A method according to Claim 34 wherein said DNA
construct is pMAX-4 or pElatB.

41. A method according to Claim 35 wherein said DNA

construct is pMAX-4 or pElatB.

42. A method according to Claim 36 wherein said DNA
construct is pMAX-4 or pElatB.

43. A method according to Claim 37 wherein said DNA
construct is pMAX-4 or pElatB.

44. A method according to Claim 38 wherein said DNA
construct is pMAX-4 or pElatB.

45. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said DNA sequence is integrated by illegitimate recom-bination or by homologous recombination.

46. A method according to Claim 34 wherein said DNA
sequence is integrated by illegitimate recombination or by homologous recombination.

47. A method according to Claim 35 wherein said DNA
sequence is integrated by illegitimate recombination or by homologous recombination.

48. A method according to Claim 36 wherein said DNA
sequence is integrated by illegitimate recombination or by homologous recombination.

49. A method according to Claim 37 wherein said DNA
sequence is integrated by illegitimate recombination or by homologous recombination.

50. A method according to Claim 38 wherein said DNA
sequence is integrated by illegitimate recombination or by homologous recombination.

51. A method according to Claim 39 wherein said DNA
sequence is integrated by illegitimate recombination or by homologous recombination.

52. A method according to Claim 40, 41, 42, 43 or 44 wherein said DNA sequence is integrated by illegitimate recombination or by homologous recombination.

53. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said DNA construct further comprises a temperature sensitive origin of replication.

54. A method according to Claim 34, wherein said DNA construct further comprises a temperature sensitive origin of replication.

55. A method according to Claim 35, wherein said DNA construct further comprises a temperature sensitive origin of replication.

56. A method according to Claim 36, wherein said DNA construct further comprises a temperature sensitive origin of replication.

57. A method according to Claim 37, wherein said DNA construct further comprises a temperature sensitive origin of replication.

58. A method according to Claim 38, wherein said DNA construct further comprises a temperature sensitive origin of replication.

59. A method according to Claim 39, wherein said DNA construct further comprises a temperature sensitive origin of replication.

60. A method according to Claim 40, 41, 42, 43 or 44, wherein said DNA construct further comprises a temperature sensitive origin of replication.

61. A method according to Claim 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

62. A method according to Claim 34, wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

63. A method according to Claim 35, wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

64. A method according to Claim 36, wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

65. A method according to Claim 37 I wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

66. A method according to Claim 38, wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

67. A method according to Claim 39, wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

68. A method according to Claim 40, 41, 42, 43 or 44, wherein said DNA construct further comprises a temperature sensitive plasmid derived from plasmid pE194.

69. Bacillus PBT108, PBT122 or T13F.